Electronic products have become progressively more complex, driven at least in part by the demand for enhanced functionality and smaller sizes. While the benefits of enhanced functionality and smaller sizes are apparent, achieving these benefits also can create problems. In particular, electronic products typically have to accommodate a high density of semiconductor devices in a limited space. For example, the space available for processors, memory devices, and other active or passive devices can be rather limited in cell phones, personal digital assistants, laptop computers, and other portable consumer products. In conjunction, semiconductor devices are typically packaged in a fashion to provide protection against environmental conditions as well as to provide input and output electrical connections. Packaging of semiconductor devices within semiconductor device packages can take up additional valuable space within electronic products. As such, there is a strong drive towards reducing footprint areas taken up by semiconductor device packages. One approach along this regard is to stack semiconductor device packages on top of one another to form a stacked package assembly, which is also sometimes referred as a package-on-package (“PoP”) assembly.
FIG. 1 illustrates a stacked package assembly 100 implemented in accordance with a conventional approach, in which a top package 102 is disposed above and electrically connected to a bottom package 104. The top package 102 includes a substrate unit 106 and a semiconductor device 108, which is disposed on an upper surface 118 of the substrate unit 106. The top package 102 also includes a package body 110 that covers the semiconductor device 108. Similarly, the bottom package 104 includes a substrate unit 112, a semiconductor device 114, which is disposed on an upper surface 120 of the substrate unit 112, and a package body 116, which covers the semiconductor device 114. Referring to FIG. 1, a lateral extent of the package body 116 is less than that of the substrate unit 112, such that a peripheral portion of the upper surface 120 remains exposed. Extending between this peripheral portion and a lower surface 122 of the substrate unit 106 are solder balls, including solder balls 124a and 124b, which are initially part of the top package 102 and are reflowed during stacking operations to electrically connect the top package 102 to the bottom package 104. As illustrated in FIG. 1, the bottom package 104 also includes solder balls 126a, 126b, 126c, and 126d, which extend from a lower surface 128 of the substrate unit 112 and provide input and output electrical connections for the assembly 100.
While a higher density of the semiconductor devices 108 and 114 can be achieved for a given footprint area, the assembly 100 can suffer from a number of disadvantages. In particular, the relatively large solder balls, such as the solder balls 124a and 124b, spanning a distance between the top package 102 and the bottom package 104 take up valuable area on the upper surface 120 of the substrate unit 112, thereby hindering the ability to reduce a distance between adjacent ones of the solder balls as well as hindering the ability to increase a total number of the solder balls. Also, manufacturing of the assembly 100 can suffer from undesirably low stacking yields, as the solder balls 124a and 124b may not sufficiently adhere to the substrate unit 112 of the bottom package 104 during reflow. This inadequate adherence can be exacerbated by molding operations used to form the package body 116, as a molding material can be prone to overflowing onto and contaminating the peripheral portion of the upper surface 120. Moreover, because of the reduced lateral extent of the package body 116, the assembly 100 can be prone to bending or warping, which can create sufficient stresses on the solder balls 124a and 124b that lead to connection failure.
It is against this background that a need arose to develop the stackable semiconductor device packages and related stacked package assemblies and methods described herein.